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The cabling of the industrial communication systems (Modbus RS485) is different in some ways from the cabling used for power cabling and the electrician may experience some difficulties if he is not an expert in Modbus communication networks. The main difference is, that pin 1 and 6 on the RJ11 socket of the MJ20-PRG module are used as power supply. To get the solar PV power from the roof down to the basement shed, we purchased 20 meters of 6mm armoured cable; this was routed down the back of the house and into the shed through the stone wall. This has thick stone walls and a concrete ceiling and has space to install 2 inverters and a battery system later if required. Each sensor has two mounting holes for attaching it to walls and other surfaces. Below you will see a cabling example for one master and two slaves in a full-duplex and a half-duplex situation.

To minimise shadows over the top row of panels, we decided to mount 2 on the top row and 3 below, which will give us a theoretical maximum output of 1.6kW, which is suitable for the Solis Solar 1.5kW Mini 5G Inverter. The data COM port on the base of the Solis inverter uses a small round 4-pin plug with a screw thread to hold it in place when connected. The adapter was placed under the microscope, and we traced the data A & B lines from the plug to the RS485 chip on the PCB. BTX/BRX. It incorporates an FTDI RS485-to-USB converter chip which is compatible with all versions of Windows. If your PC or controller only has RS232 port then you need an RS232 to RS485 converter or adapter for your PC or controller. This module is powered by the RS232 port from the connecting computer. These pins have to be connected to handshaking outputs at the PC side on the RS232 port. What cable should I use to connect meters with an RS485 port to the USB port of a PC?

Then use front panel programming to set the baud rate, protocol, digital address, half or full duplex, and other available parameters. Both boards support the Modbus protocol and Laurel’s Custom ASCII protocol, as well as half-duplex or full-duplex RS485 communications. If multiple analog input meters or transmitters are digitally addressed in command mode on an RS485 line using the Modbus RTU protocol or the Custom ASCII protocol, the rate becomes about 2 readings per second. Set the PC to N81 for the Custom ASCII protocol, or to N82 or E81 for the Modbus RTU protocol. A single analog input meter or transmitter can stream readings to a PC at up to 60 readings per second and the Custom ASCII protocol set to continuous (or streaming) model. See page 7 of the Laurel digital panel meter manual, page 7 of the Laurel counter manual, page 8 of the Laurel scale meter manual, or page 8 of the Custom ASCII protocol manual. When a single RS485 meter or counter is connected to a PC via a cable CBL06, set the PC to 9600 baud. The RS485 system used for Modbus communication provides a main cable (Bus or backbone), to which all the devices have to be connected with branches (also known as stubs) that are as short as possible.

The maximum number of repeaters that should be serially connected is 3. A higher number introduces excessive delays in the communication system. In order to increase the extent of the Modbus network, rs485 cable repeaters can be used; and signal amplifying and regenerating devices provided with two communication ports that transfer to each what they receive from the other. Longer branches could cause signal reflections and generate disturbances and consequent errors in the reception of data. We found that there are 10K ohm resistors fitted on the A & B data lines with the A channel having a 10K pull-up resistor to 3.3 volts and the B channel having a 10K pull-down resistor to ground. We found panels produced by JA Solar which are 1689 x 996mm and have a 330W output, and we could fit 5 or 6 of these on the roof between the chimneys. The drivers of RS485 are tristate: Mark, Space and Off. Not more than one breakout board is required per RS485 line. Can I add an RS485 board to a meter later? Is there an easy way to log data to a PC from multiple instruments on an RS485 bus?